Nuclear radiation detection device utilizing diamond detector with injecting and blocking contacts

ABSTRACT

A device for detecting nuclear radiations, comprising a nuclear radiation detector on the basis of a diamond crystal plate, having a blocking and an injecting contacts, a detector power supply associated with the injecting contact, and an amplifier with recording means associated with the blocking contact.

United States Patent [15] 3,668,400 Kozlov 1 June 6, 1972 NUCLEARRADIATION DETECTION [56] References Cited DEVICE UTILIZING DIAMONDDETECTOR WITH INJECTING UNIIED STATES PATENTS AND BLOCKING CONTACTS2,678,400 5 1954 McKay ....2so/s3.3 x I 2,694,112 11/1954 McKay....250/83.3 X [72] lnventor: Stanislav Fedorovich Kozlov, B. 2,760,0788/1956 Youmans. ....250/83.3 Akademicheskaya ulitsa, 49, korpus 1, RV.2,806,145 9/1957 Cotty ..250/83.3 18, Moscow, USSR.

Primary Examiner-Archie R. Borchelt [22] Filed Sept 1969Attorney-Waters, Roditi, Schwartz & Nissen [211 App]. No.: 856,606

[57] ABSTRACT [30] Foreign Application Priority Data A device fordetecting nuclear radiations, comprising a nuclear radiation detector onthe basis of a diamond crystal Sept. I 1, I968 plate, h i g a blockingand an j i g contacts, a detector power supply associated with theinjecting contact, and an am- [52] LS. CI. ..250/83.3 R, 250/83 R ifiwith recording means associated i the blocking [51] Int.Cl. ..G0lt 1/24tact [58] Field of Search ..250/83, 83.3 R

1 Claim, 2 Drawing Figures PATENTEnJux 6 I972 3, 668 400 p0 war supplyrem/ding means ampli fier 1 NUCLEAR RADIATION DETECTION DEVICE UTILIZINGDIAMOND DETECTOR WITH INJECTING AND BLOCKING CONTACTS The presentinvention relates to the devices for nuclear radiation detection,comprising a diamond detector as an element sensitive to nuclearradiation.

In modern practice devices are widely used for detecting nuclearradiations, comprising as a radiation sensitive element germanium orsilicon detectors with two contacts. Such devices also contain adetector power supply and an amplifier with recording means. One of thedetector contacts is usually grounded, while the opposite contactassociated with the power supply is used for removing the detectorsignals arising from bombardment with nuclear radiation. For thispurpose it is connected through a blocking capacitor to the amplifierwith the recording means.

A limitation of such devices is that it is necessary-to use guard ringsand blocking capacitors at the amplifier input, since the detector hasleakage currents. This increases the device input capacitance and henceresults in decreasing the input signal and the sensitivity of the deviceas a whole.In addition, the devices described above cannot operatereliably and efficiently at elevated temperatures owing to a high noiselevel of the detector. Attempts have been made with a view to developinga device for nuclear radiation detection, comprising a diamond crystalas a detector. However, such devices have not found practicalapplication, since the previously known diamond detectors had poorcounting and spectrometric properties and polarized under prolongedirradiation.

We have proposed a new detector on the basis of a diamond crystal plate(see our application Ser. No. 716,953). Compared with the known diamonddetectors, the counting and spectrometric properties of this detectorare much better. Although this detector used in the device for nuclearradiation detection may be associated with the power supply and theamplifier in the usual fashion, the known connection circuit does notallow, however, all its capabilities to be fully realized.

It is an object of the present invention to increase the sensitivity andreliability of the device designed for detection of nuclear radiation.

In the accomplishment of said and other objects of the invention, in adevice for detecting nuclear radiations, comprising a nuclear radiationdetector with an amplifier and means for recording output signals and apower supply, according to the invention, a detector is essentially adiamond crystal plate with contacts formed at the opposite sidesthereof, having the thickness of the operating range between saidcontacts not exceeding the distance travelled by charge carriers in thediamond crystal under the influence of an applied electric field, thecontact disposed on the plate side adapted to be irradiated being madeblocking in relation to charge can'iers and connected to the input of anamplifier with recording means, while the opposite contact disposed onthe plate side not adapted to be irradiated is made of a materialcapable, in conjunction with a diamond, of injecting charge carriersunder the influence of an applied electric field and connected through aresistor to a power supply.

Under operation the signal voltage at the amplifier input is given by UQ/ZC where Q is the electrical charge collected into the detectorcontacts and 2C is the total input capacitance to earth, equal to EC CdCs Ca Here Cd is the detector capacitance, Cs is the stray capacitanceand C is the amplifier input capacitance. The diamond detectorcapacitance Cd is small and stable. The

diamond detector leakage currents are negligible owing to these reasons,the proposed device connection circuit allows the total inputcapacitance EC to be considerably reduced. This provides for obtaining alarge signal and a high signal to noise ratio and increases the devicesensitivity and counting efiiciency.

For a better understanding of the invention presented hereinbelow is adescription of an exemplary embodiment thereof with reference to theaccompanying drawing, in which a schematic of the device for detectingnuclear radiations is shown in accordance with the invention.

A nuclear radiation detector I is mounted in a metal housing 2 having awindow opening 3. The detector 1 is essentially a diamond crystal plate4, on whose opposite sides contacts 5 and 6 are provided. The detector lis arranged so that the contact 5 faces the window opening 3 throughwhich nuclear radiation under investigation falls on the detector 1. Thecontact 5 is made blocking in relation to charge carriers, for examplein the form of a gold film. The contact 6 disposed on the opposite sideof the plate 4 is made of a material capable, in conjunction with adiamond, of injecting charge carriers under the influence of an appliedelectric field. For instance this contact may be formed by doping thesurface layer of the diamond crystal plate with boron. The thickness dof the operating range of said plate 4 between the contacts 5 and 6 doesnot exceed the-distance travelled by charge carriers in the diamondcrystal under the influence of an applied electric field and is given byd s 8= m-E where 1; is the mobility of charge carriers (electrons orholes), 1' is the lifetime of charge carriers, E is the applied fieldstrength, 8 is the distance travelled by charge carriers under theinfluence of the applied electric field.

The detector I is fixed on a support 7 for instance by means of silverpaint (paste) subjected to appropriate treatment. The

support 7 made from an electroconductive material is disposed on theside of the injecting contact 6. The housing 2 has insulators 8 and 9.Metal leads l0 and 11 extend through these insulators. A metal lead 12is used for grounding the housing 2. The lead 10 welded to the support 7is associated through a resistor 13 with a power supply 14. The lead lljoined to the blocking contact 5 is connected by a short wire to theinput of an amplifier 15 with recording means 16.

The device described hereinabove operates in the following manner. Adirect voltage is applied to the diamond detector I with the aid of thepower supply 14. Nuclear radiation passes through the window opening 3in the housing 2, penetrates the diamond detector I from the side of theblocking contact 5 and causes ionization inside the detector. Theresulting charge carriers (electrons and holes) move to the contacts 5and 6 under the influence of the applied electric field. The electronstravel to the injecting contact 6, if the positive potential is appliedto it. The holes travel to the blocking contact 5. On their movement tothe contact 6 some electrons are trapped by traps always present in thediamond crystal. As a result, the diamond crystal plate 4 polarizes. Theinjecting contact 6 is designed to remove said polarization. Since deeptraps are present in the diamond, the injection currents from thecontact 6 are limited by the space charge accumulated by these traps.Thus, the injection currents do not induce significant conductivity and,consequently, noise. However, when field and charge equilibrium insidethe diamond crystal plate is disturbed due to polarization created byincident nuclear radiation, the charge carriers (holes) injected by thecontact 6 restore the initial steady state of the crystal.

Some holes travelling to the contact 5 may also be trapped. In thiscase, however, the trapped holes are in the ionization zone and can beneuu'alized by the charge carriers of the opposite sign, i.e. byelectrons. In addition, when detecting heavily ionizing nuclearradiation, losses in the electron-hole plasma are reduced, since thefield strength is higher in the vicinity of the blocking contact 5.

The signal removed from the blocking contact 5 of the diamond detector 1is fed to the input of the amplifier l5 and 3 then to the recordingmeans 16, such as a pulse-height analyser.

The diamond detector can also be enclosed in a non-metal housing made,for example, from ceramics or plastics. If the housing is made fromceramics, it is.possible to elevate the upper limit of allowableoperating temperatures. If the housing is made from plastics or metalshaving a low atomic number, such as aluminum, the device has reducedsensitivity to gamma-radiation background. The diamond detector may alsobe encapsulated in epoxy resins, silicone resins or com- Mm- With a viewto increasing the detecting area, a mosaic is composed of the diamonddetectors with the blocking and injecting contacts.

A For long-range radiation spectrometry the diamond detectors may bestacked together, the stack thickness exceeding the range of incidentnuclear radiation.

The present device for detecting nuclear radiations has a number ofadvantages over known devices. It allows difl'erent types of radiationshaving various energies to be detected with high sensitivity andreliability, posseses good counting andspectrometric properties andoperates at room and higher temperatures with a high signal to noiseratio. Since the diamond detector withstands heating up to hightemperatures, the defects caused by nuclear radiations may be annealedfrom time to time. This increases radiation resistance of the device.

We claim: 1

l. A device for detecting nuclear radiations, compr'uing in combinationa nuclear radiation diamond detector, said detector being essentially adiamond crystal plate having contacts disposed at the opposite sidesthereof, said plate having a thickness equal to or less than the maximaldrift length of charge carriers in the diamond crystal under theinfluence of an applied electric field, the contact disposed on theplate side subjected to radiation being made blocking in relation tocharge carriers, the opposite contactdisposed on the plate side notsubjected to radiation being made of a material caps-- ble, inconjunction with the diamond, of injecting charge car riers under theinfluence of said applied electric field; a power supply connected tosaid injecting contact; an amplifier connected to said blocking contact;and means for recording generated output signals from said amplifier.

i l l i t

1. A device for detecting nuclear radiations, comprising in combinationa nuclear radiation diamond detector, said detector being essentially adiamond crystal plate having contacts disposed at the opposite sidesthereof, said plate having a thickness equal to or less than the maximaldrift length of charge carriers in the diamond crystal under theinfluence of an applied electric field, the contact disposed on theplate side subjected to radiation being made blocking in relation tocharge carriers, the opposite contact disposed on the plate side notsubjected to radiation being made of a material capable, in conjunctionwith the diamond, of injecting charge carriers under the influence ofsaid applied electric field; a power supply connected to said injectingcontact; an amplifier connected to said blocking contact; and means forrecording generated output signals from said amplifier.